A conventional muffler of an internal combustion engine is disclosed in, for example, Japanese Patent Laying-Open No. 2000-54822, directed to reducing the size without degradation in the muffling performance. The muffler disclosed in this publication includes a control valve that opens when the pressure of the exhaust gas in the muffler chamber exceeds a predetermined level. A valve opening that communicates with the muffler chamber and a sheet-like valve capable of deformation and provided so as to close the valve opening, constitute the control valve.
Japanese Patent Laying-Open No. 9-32590 discloses a throttle valve device for an internal combustion engine, directed to allowing resin-molding of the throttle body and preventing freezing of the throttle valve. Japanese Patent Laying-Open No. 2002-4893 discloses a throttle body employing resin as the material, and directed to reliably preventing freezing with a simple configuration.
Japanese Patent Laying-Open No. 2000-328935 discloses an exhaust noise silencer for a vehicle, directed to obviating freezing of condensed water in the outlet pipe and preventing blocking of the exhaust system. The exhaust noise silencer disclosed in this publication includes an inlet pipe and an outlet pipe with a pipe portion formed inclined with respect to the horizontal level. The inlet pipe and outlet pipe each have an opening at individual chambers within the muffler, divided by a partition.
The muffler disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-54822 has the control valve provided on the flowing path of exhaust gas to open/close corresponding to change in the pressure of the exhaust gas. A muffler provided with such a valve is disadvantageous in that condensed water of the exhaust gas remains in the proximity of the valve after the engine has been started. If the engine is then stopped and left under such a state, the condensed water will freeze at low temperature conditions such as during wintertime, leading to the possibility of malfunction in the valve.